This article discusses Niklas Luhmann's understanding of complexity, its role in theory, and the different ways for its use. It starts from a paradigmatic change that took place in the field of Science in general after the rupture of the Newtonian model. In the 20th century, the paradigm of order, symmetry, regularity, and regulation of the intellect over things enters a crisis. After new formulation in Physics, Chemistry, etc, a new universe emerges over the bases radically opposed to those of modern Science. There is rehabilitation of chaos, process irreversibility, indeterminism, the observer, and complexity. That new conceptual environment served as the substrate for Niklas Luhmann's theoretical reflection. Through the Theory of the Social systems, the author proposes the reduction of the world's complexity. The role of social systems is to reduce complexity by its difference regarding the surroundings. By reducing complexity, on the other hand, he also builds his own complexity. Luhmann sees complexity when it is no longer possible that each element relates in any moment to all others. Complexity forces selection, which means contingency and risk. Luhmann further discusses the concept of complexity by introducing the figure of the observer and the distinction of complexity as the unity of a multiplicity. He also deals with the limit of relationship connections, the time factor, self-reference of the operations, and representation of complexity as meaning. Finally, the article deals with complexity in the system of science, the way it reduced internal and external complexity according to its own operative basis.
complexity; social systems; science; complex world; system and surroundings; autopoiesis; second-order observation; interdisciplinarity; trans-disciplinarity; multidisciplinarity